The present application relates to a head-mounted display (HMD) worn on the head of an observer and including a frame shaped like glasses and an image display apparatus.
Japanese Unexamined Patent Application Publication No. 2006-162767 discloses a virtual-image display apparatus (image display apparatus) in which a virtual-image optical system allows an observer to view, as an enlarged virtual image, a two-dimensional image formed by an image forming device.
FIG. 3 is a conceptual view of such an image display apparatus. Referring to FIG. 3, an image display apparatus 100 includes an image forming device 111 having a plurality of pixels arranged in a two-dimensional matrix, a collimating optical system 112 for collimating light emitted from the pixels of the image forming device 111, and a light guide device (optical device) 120 on which the light collimated by the collimating optical system 112 is incident. The incident light is guided and emitted from the light guide device 120. An image generating device 110 is constituted by the image forming device 111 and the collimating optical system 112. The light guide device 120 includes a light guide plate 121, a first deflecting member 130 (e.g., a single-layer light reflective film), and a second deflecting member 140 (e.g., a light reflective multilayer film having a layered structure). Incident light propagates in the light guide plate 121 by total reflection and is then emitted from the light guide plate 121. The first deflecting member 130 reflects the light incident on the light guide plate 121 so that the incident light is totally reflected in the light guide plate 121, and the second deflecting member 140 emits the light, which propagates in the light guide plate 121 by total reflection, from the light guide plate 121.
Further, Japanese Unexamined Patent Application Publication No. 2007-94175 discloses a virtual-image display apparatus (image display apparatus) using a hologram diffraction grating, in which a virtual-image optical system allows an observer to view, as an enlarged virtual image, a two-dimensional image formed by an image forming device.
FIG. 5A is a conceptual view of such an image display apparatus. Referring to FIG. 5A, an image display apparatus 300 basically includes an image forming device 111 for displaying an image, a collimating optical system 112, and a light guide device (optical device) 320 on which the light displayed by the image forming device 111 is incident. Incident light is guided to the eye 41 of the observer. The light guide device 320 includes a light guide plate 321, and first and second diffraction grating members 330 and 340 provided on the light guide plate 321. Each of the first and second diffraction grating members 330 and 340 is formed by a reflective volume hologram diffraction grating. Light emitted from pixels in the image forming device 111 enters the collimating optical system 112, where the light is converted into parallel light, and the parallel light enters the light guide plate 321. The parallel light is incident on and is emitted from a first surface 322 of the light guide plate 321. On the other hand, the first and second diffraction grating members 330 and 340 are mounted on a second surface 323 of the light guide plate 321 parallel to the first surface 322.
The image display apparatus constituted by the image generating device 110 and the light guide device 120 or 320 is attached to a frame shaped like glasses. Specifically, for example, as shown in FIG. 14, two image generating devices 110 are fixed to opposite ends of a front portion 1011 of a frame 1010 shaped like glasses via fixing members 1017 (see FIG. 1 of Japanese Unexamined Patent Application Publication No. 2006-162767).